In a focal plane camera shutter a leading blade for opening the shutter and a trailing blade for closing the shutter are customarily operated by individual actuating members each biased by a driving spring. For proper shutter operation it is desirable to lessen the unevenness of exposure and to equalize the running speeds of both blades. However, due to manufacturing tolerances it is difficult to equalize the driving force applied to both of the actuating members.
Also, the speed or the driving force of the opening member for starting an exposure directly affects the exposing time of the shutter. In the case of an electronic shutter, the start of the time-control function of the electronic circuits is affected while in the case of a mechanical shutter the working time of delaying mechanism is controlled. Accordingly, in order to control exposure time exactly, measures are necessary to compensate the performance deterioration due to errors in the manufacture of the individual actuating elements by adjusting the driving force acting on such elements.